I pointed out earlier in this thread that with a completely balanced design you are locked into this circuit and it's disadvantages, no matter what. I also mentioned that the best way to get around this state of affairs is to have an unbalanced amplifier, but offer a balanced input only which can be bypassed if desired.

This gives all the advantages of noise cancellation offered by a balanced interconnection, but provides a more pure signal path at the same time. If somebody does not want to use the balanced feature, they can simply bypass it completely. You can't do this if the entire circuit is balanced.

The fact is, once the cable is terminated into a summing amplifier as in the input to a balanced amplifier, the noise picked up by that cable is nulled out - having the rest of the amplifier's circuitry balanced will not cancel noise any more than when the input only is balanced.

It is the function of the amplifier's chassis and it's shielding to reject noise which is trying to make it's way into the inside the amplifier. In any event, the signal levels within a power amplifier are far, far higher than as is the case in interconnects so that the signal will be that much higher above any potential interferrence.

I am suprised by ATI's candidness on this issue, but what they say about the audibility of distortion is off base. Yes it is true that distortion is not generally audible until it reaches 1%, but this is only true of the even order ones!

Odd order distortion is audible at far lower levels, especially ones above the 5th order as a hardening, sterility and harshness of the sound.

I am talking about levels of odd order harmonic distoriton in the .00X% range here - this is not a moot point!

Additionally, the .003% distoriton rating that ATI cites is taken at the point in the amplifier's power curve where distoriton is lowest - in the case of a 100 watt amplifier, this would be roughly 60 watts. If you look at any solid state power amplifier's power verses distortion curve, you will see that distortion rises rapidly at low and high power levels.

The distortion at the power levels you typically listen at, and the levels where the amplifier operates 90% of the time is around 1 watt.

Any distortion present at this level is critical, as the ratio of distortion to signal (music, film soundtrack) is much less. This is precisely where you want any distortion present to be benign. In other words you want any distortion at normal operating levels to be predominately even order, not harsher high order/odd order distortion.

It is also fact that the presence of the even order harmonic distortion elements, especially the 2nd, will mask the higher order ones and render them more benign. Of all the distortion elements (and you must have distortion in all electronics), you certainly do not want to get rid of the ones that are helping to reduce the audibility of the harsher distoriton elements!

I've brought up the example of tube amplifiers before. They typically produce almost exclusively even order distortion, most of it of the 2nd order - the most benign of all. What presence of the 3rd harmonic there is, it's audibility is completely swamped by the presence of the strong 2nd order distortion component.

This is a major reason why tube amps sound so natural.